index.css

.flex-container {
    display: flex;
    flex-direction: row;
    font-size: 30px;
    text-align: center;
    max-width: 50%;

    gap: 5px;

    margin-bottom: 5px;
}
  
.flex-item {
    display: block;
    background-color: #555555;
    color: #fff;
    padding: 10px;

    flex: 50%;

    border: 2px solid #555555;
    text-decoration: none;

    transition: background-color 0.4s ease, border-color 0.4s ease, color 0.4s ease;
}

.flex-item--warning {
    background-color: #000;
    border-color: #000;
}

.flex-item.flex-item--warning:hover {
    background-color: #fff;
    color: #000;
}

.flex-item:hover {
    background-color: #fff;
    color: #555555;
}

@media (max-width: 800px) {
    .flex-container {
      flex-direction: column;
      max-width: 100%;
    }
}